1. Field of the Invention
The present invention relates to a semiconductor device which in particular contains a semiconductor element having a hollow construction.
2. Background Information
In recent years, a type of semiconductor element having a hollow region inside for enabling a portion of the element to be displaced, such as a semiconductor acceleration sensor chip using an MEMS (micro electro mechanical system), has come to be widely used. In the following, this type of semiconductor element will be referred to as a hollow construction semiconductor element.
One typical kind of hollow construction semiconductor element would be a semiconductor acceleration sensor chip, as mentioned above. Normally, a semiconductor acceleration sensor chip is housed in the interior of a package made of ceramic, and is structured in a way such that acceleration can be detected using a piezoresistive effect, i.e., a phenomenon in which a resistance value changes in proportion to a generated stress.
To be more precise, a typical semiconductor acceleration sensor chip comprises a fixing portion, a spindle body and multiple beams, for instance. Each beam has flexibility, and has one end thereof fixed to the fixing portion and the other end thereof fixed to the spindle body, while keeping the spindle body in a movable state with respect to the fixing portion. These beams have piezoresistive elements attached thereto, respectively, and by having these piezoresistive elements connected among one another through wiring patterns, a Wheatsone bridge circuit can be established.
In a semiconductor acceleration sensor chip having such hollow construction, when there is a change in speed, the beams will bend due to the stress generated by the inertial movement of the spindle body. At the same time, the piezoresistive elements attached to the beams will also bend. Due to such bending, the resistance value of each piezoresistive element will change, resulting in a change in the resistance balance in the Wheatsone bridge. Acceleration can be detected by measuring such change in the resistance balance as a current change or a voltage change.
Such semiconductor acceleration sensor chip as described above is usually fixed to the bottom of the cavity inside the package using an adhesive material or the like. However, when the semiconductor acceleration sensor chip is fixed directly to the package, there is a possibility that residual stress will be generated due to the heat produced when a wire bonding process is performed for connecting the electrode pads of the semiconductor acceleration chip and electrode pads of the package, and when a die-bonding process is performed for fixing the package for housing the semiconductor acceleration sensor chip to a circuit substrate, etc., for instance.
For example, Japanese Laid-Open Patent Application No. 2004-309188 (hereinafter to be referred to as patent reference 1) discloses a certain structure which copes with such problem.
Patent reference 1 introduces a structure in which steps having top faces that are higher than the bottom face of the cavity inside the package are formed on the sides of the cavity, the sides of the semiconductor acceleration sensor chip are flanged, and the flanged parts are fixed to the steps, and thus, the semiconductor acceleration sensor chip is fixed inside the package.
On the other hand, Japanese Laid-Open Patent Application No. 2005-127750 (hereinafter to be referred to as patent reference 2) introduces a structure in which the semiconductor acceleration sensor chip is bonded to the package using flip-chip technology. According to patent reference 2, it is possible to miniaturize the apparatus including the package as a whole.
In the case of fixing a semiconductor element with a hollow construction such as a semiconductor acceleration sensor chip directly to the package, there is a possibility that the characteristics of the semiconductor element will be changed because deformation of the package due to external stress, heat expansion, etc. can be easily transmitted to the semiconductor element, and this may result in inducing malfunction. Moreover, since the heat expansion coefficient is different between the package and the semiconductor element, stress is generated between the package and the semiconductor element after heating, and this may change the characteristics of the semiconductor element, resulting in inducing malfunction.
The structure as disclosed in patent reference 1 includes some parts where the package and the semiconductor element (i.e., the semiconductor acceleration sensor chip) are directly attached to each other. Therefore, deformation of the package will be transmitted to the semiconductor element through the attaching parts, which may result in changing the characteristics of the semiconductor element.
The structure as disclosed in patent reference 2, the semiconductor element (i.e., the semiconductor acceleration sensor chip) is directly bonded to a portion of the package using flip-chip technology. Therefore, deformation of the package is transmitted to the semiconductor element through the boding parts, which may result in changing the characteristics of the semiconductor element. Moreover, due to the heat expansion coefficient being different between the package and the semiconductor element, stress may be generated between the package and the semiconductor element after heating, which may result in changing the characteristics of the semiconductor element and inducing malfunction.
In view of the above, it will be apparent to those skilled in the art from this disclosure that there exists a need for an improved semiconductor device. This invention addresses this need in the art as well as other needs, which will become apparent to those skilled in the art from this disclosure.